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Nuclear Physics Fundamental Principles - Glossary

A

ABSORBED DOSE
Absorbed dose is the amount of energy deposited in any material by ionizing radiation. It is a measure of energy absorbed per gram of material. The SI unit of absorbed dose is the gray. The special unit of absorbed dose is the rad.

ACCURACY
The degree of agreement between an individual measurement or average of measurements and the accepted reference value of the quantity being measured. See also precision.

ACTIVATION ANALYSIS
A method of chemical analysis (for small traces of material) based on the detection of characteristic radionuclides in a sample after it has been subjected to nuclear bombardment.

ADC
Analog to Digital Converter. A device which changes an analog signal to a digital signal.

AIM
Acquisition Interface Module: a type of multichannel analyzer.

ALARA
Since exposure to radiation always carries some risk, the exposure should be kept "As Low As Reasonably Achievable", as defined by 10 CFR 20.

ALGORITHM
A set of well-defined rules for solving a problem.

ALPHA PARTICLE [Symbol: a]
A particle made up of two neutrons and two protons; it is identical to a helium nucleus and is the least penetrating of the three common types of radiation(the other two are beta particles and gamma rays), being stopped by a sheet of paper or a few centimeters of air. An alpha-emitting substance is generally not dangerous to a biological system, such as the human body, unless the substance has entered the system. See decay.

AMPLIFICATION
The process by which weak signals, such as those from a detector are magnified to a degree suitable for measurement.

ANALOG MULTIPLEXER
An electronic instrument that accepts several inputs and stores each one in a separate section of MCA memory. Also called a mixer/router.

ANNIHILATION RADIATION
Radiation produced by the annihilation of a positron and an electron. For particles at rest, two photons with an energy of 511 keV each are produced.

ANTICOINCIDENCE CIRCUIT
A circuit with two inputs. The circuit delivers an output pulse if one input receives a pulse within a predetermined time interval, usually on the order of milliseconds, but not if both inputs receive a pulse. A principle used in pulse height analysis. See also coincidence circuit.

AREA
The number of counts in a given region of a spectrum that are above the continuum level.

ASCII
An acronym for American Standard Code for Information Interchange, a method for encoding alphabetical, numeric, and punctuation characters and some computer control characters.

ATTENUATION CORRECTION
Correction to the observed signal for the attenuation of radiationin a material between the sample and the detector or within the sample itself.

B

BACKGROUND RADIATION
radiationdue to sources other than the sample, such as cosmic rays, radioactive materials in the vicinity of a detector or radioactive components of the detection system other than the sample.

BACKGROUND SUBTRACTION
The statistical process of subtracting the background level of radiationfrom a sample count.

BACKSCATTERING
The process of scattering or deflecting into the sensitive volume of a measuring instrument radiationthat originally had no motion in that direction. The process is dependent on the nature of the mounting material, the shield surrounding the sample and the detector, the nature of the sample, the type of energy of the radiation, and the geometry. See also scattering.

BASELINE
In biology, a known base state from which changes are measured. In electronics, a voltage state (usually zero volts) from which a pulse excursion varies.

BECQUEREL [Symbol: Bq]
The SI unit of activity, defined as one disintegration per second (dps).

BETA PARTICLE [Symbol: ]
An elementary particle emitted from a nucleus during radioactive decay with a single electrical charge and a mass equal to 1/1837 that of a proton. A negatively charged beta particle is identical to an electron. A positively-charged beta particle is called a positron.

BIOLOGICAL HALF-LIFE [Symbol: Tb]
The time required for a biological system to eliminate half of the amount of a substance (such as radioactive material) by natural processes. Compare effective half-life and half-life.

BLUETOOTH
Bluetooth is a wireless protocol utilizing short-range communications technology facilitating data transmissions over short distances from fixed and/or mobile devices, creating wireless personal area networks (PANs).

BREMSSTRAHLUNG
radiationproduced by the sudden deceleration of an electrically charged particle when passing through an intense electrical field.

C

CASCADE SUMMING
Also referred to as true coincidence summing, it occurs when two or more pulses from the same decay are summed because they deposit energy in the detector at the same time. It is a function of the measurement efficiencies and occurs only with susceptible cascading nuclides (60Co, 88Y, 152Eu, 133Ba, etc.)

CENTROID
The center of a peak; usually not an exact channel number.

CHANNEL
One of an MCA's memory locations for storage of a specific level of energy or division of time.

CHERENKOV RADIATION
Photons emitted from polarized molecules when returning to their ground state following excitation by charged particles traveling faster than the speed of light in a transparent medium.

CHI-SQUARE TEST
A general procedure for determining the probability that two different distributions are actually samples of the same population. In nuclear counting measurements, this test is frequently used to compare the observed variations in repeat counts of a radioactive sample to the variation predicted by statistical theory.

COINCIDENCE CIRCUIT
A circuit with two inputs. The circuit delivers an output pulse if both inputs receive a pulse within a predetermined time interval, usually on the order of milliseconds, but not if just one input receives a pulse. A principle used in pulse height analysis. See also anticoincidence circuit.

COINCIDENCE SUMMING
A process where the signal from two or more gamma rays emitted by a single decay of a single radionuclide occur within the resolving time of the detector end up being recorded together as a single event so that the recorded event is not representative of the original decay. Typically causes counts to be lost from the full energy peaks, but may also cause addition to the full energy peaks. Coincidence summing is a function of the sample-to-detector geometry, and the nuclide's decay scheme. It is not a function of the overall count rate.

COLLECT
An MCA function that causes storage of data in memory.

COMPTON SCATTERING
Elastic scattering of photons in materials, resulting in a loss of some of the photon's energy.

CONFIDENCE FACTOR
It is common practice when reporting results to assign them a confidence level: the value plus or minus one standard deviation. radiationprotection measurements are usually reported at the 95% confidence level, meaning that the results would be expected to be within plus or minus that range 95 out of 100 times. Also called Confidence Level.

CONTINUUM
A smooth distribution of energy deposited in a gamma detector caused by the partial absorption of energy from processes such as Compton scattering or bremsstrahlung.

CONVERSION GAIN
The number of discrete voltage levels (or channels) that the ADC's full scale input is divided into.

CONVERSION TIME
The time required to change an input signal from one format to another, such as analog to digital, or time difference to pulse amplitude; contributes to dead time.

COSMIC RAYS
radiation, both particulate and electromagnetic, that originates outside the earth's atmosphere.

COUNT
A single detected event or the total number of events registered by a detection system.

CRITICAL LEVEL (Lc)
The level below which a net signal cannot reliably be detected. See also detection level.

CROSSOVER ENERGY
In some efficiency calibration models, the energy at which one calibration curve is changed into a second calibration curve. This is used in the Dual Efficiency Calibration in Genie software.

CURIE [Symbol: Ci]
The (approximate) rate of decay of 1 gram of radium; by definition equal to 3.7 x 1010 becquerels (or disintegrations per second). Also, a quantity of any nuclide having 1 curie of radioactivity.

D

DATASOURCE
A hardware device or a file which stores data acquisition parameters and spectral data.

DAUGHTER NUCLIDE
A radionuclide produced by the decay of a parent nuclide.

DEAD TIME
The time that the instrument is busy processing an input signal and is not able to accept another input; often expressed as a percentage. See also live time.

DECAY
The disintegration of the nucleus of an unstable atom by spontaneous fission, by the spontaneous emission of an alpha particle or beta particle, isomeric transitions, or by electron capture.

DEFAULT
The value of a parameter used by a program in the absence of a user-supplied value.

DERIVED AIR CONCENTRATION (DAC)
The concentration (Bq/m3) of a radionuclide in air that if breathed by Reference Man for a working year (2000 hours) under light activity conditions would result in the annual limit on intake (ALI) by inhalation.

DETECTION LEVEL
The level of net signal that can be predicted to be detectable. See also critical level.

DETECTOR
A device sensitive to radiationwhich produces a current or voltage pulse which may or may not correspond to the energy deposited by an individual photon or particle.

DIGITAL STABILIZATION
The monitoring of one or two reference peaks in a spectrum, one for gain and one for zero, to correct for drift in the system electronics.

DISCRIMINATOR
An electronic circuit which distinguishes signal pulses according to their pulse height or voltage so that unwanted counts can be excluded.

DISINTEGRATION
See decay.

DPM
Disintegrations per minute. One DPM equals 60 becquerels.

DOSE
The radiationdelivered to the whole human body or to a specified area or organ of the body. This term is used frequently in whole body counting applications.

DOUBLE ESCAPE PEAK
See escape peak.

E

EFFECTIVE HALF-LIFE [Symbol: Teff]
The time required for a radioactive element in a biological system, such as the human body, to be reduced by one-half as a result of the combined action of radioactive decay and biological elimination. Compare half-life and biological half-life.

EFFICIENCY
The fraction of decay events from a standard sample seen by a detector in the peak corresponding to the gamma ray energy of the emission, and stored by a detection system. Also called Peak Efficiency. Used to calibrate the system for quantitative analyses. Also used to specify germanium detectors, where the relative efficiency of the germanium detector is compared to a standard (3 x 3 in.) NaI(Tl) detector. Compare total efficiency.

EFFICIENCY CALIBRATION
A function, a lookup table, or series of functions, which correlate the number of counts seen by the detection system in specific peaks with known activity corresponding to such emission energies in a radioactive sample.

ELASTIC SCATTERING
See scattering.

ELECTRODEPOSITION
A process for coating the surface of samples being prepared for alpha spectroscopy and alpha/beta counting.

ELECTROMAGNETIC RADIATION
A general term to describe an interacting electric and magnetic wave that propagates through vacuum at the speed of light. It includes radio waves, infrared light, visible light, ultraviolet light, X rays and gamma rays.

ELECTRON [Symbol: e]
An elementary particle with a unit negative electrical charge and a mass 1/1837 that of the proton. Electrons surround the positively charged nucleus and determine the chemical properties of the atom.

ELECTRON VOLT [Symbol: eV]
The amount of kinetic energy gained by an electron as it passes through a potential difference of 1 volt. It is equivalent to 1.602 x 10-19 joules per second. It is a unit of energy, or work, not of voltage.

ENERGY CALIBRATION
A function which correlates each channel in the displayed spectrum with a specific unit of energy. Allows peaks to be identified by their location in the calibrated spectrum.

ESCAPE PEAK
A peak in a gamma ray spectrum resulting from the pair production process, the subsequent annihilation of the photons produced, and escape from the detector of the annihilation photons. If both annihilation photons escape, and the rest of the original gamma energy is fully absorbed, a double escape peak is produced at an energy equal to the original gamma ray energy minus 1.022 MeV. If only one of the photons escapes, a single escape peak is produced at an energy equal to the original gamma ray energy minus 511 keV.

EXCITED STATE
The state of molecule, atom, or nucleus when it possesses more than its ground state energy. Excess molecular or atomic energy may be reduced through emission of photons or heat. Excess nuclear energy may be reduced through emission of gamma rays or conversion electrons or by further decay of a radionuclide.

eV
See electron volt.

F

FACTORS
The parameters used by an algorithm for its calculations.

FIPS 140-2
The Federal Information Processing Standard (FIPS) Publication 140-2, FIPS PUB 140-2, is a U.S. government computer security standard used to accredit cryptographic modules.

FULL ENERGY ABSORPTION
The absorption and detection of all of the energy of an incident photon. May take place as a direct photoabsorption or as a result of multiple Compton scatterings of the incident photons within the resolving time of the detection system.

FULL ENERGY PEAK
The peak in an energy spectrum of X-ray or gamma-ray photons that occurs when the full energy of the incident photon is absorbed by the detector.

FWHM (Full Width at Half Maximum)
The full width of a peak measured at one-half of its maximum amplitude with the continuum removed. Defines the resolution of a spectroscopy system.

G

GAIN, ADC
See conversion gain.

GAIN, AMPLIFIER
The ratio of the amplifier's output signal to its input signal.

GAIN CONTROL
A control used to adjust the height of a pulse received from the detecting system.

GAMMA RAY [Symbol: ?]
A photon or high-energy quantum emitted from the nucleus of a radioactive atom. Gamma rays are the most penetrating of the three common types of radiation(the other two are alpha particles and beta particles) and are best stopped by dense materials such as lead.

GAUSSIAN FIT
Calculating the parameters of a Gaussian (or Normal) function to best match a set of empirical data (in spectroscopy, the acquired photopeak histogram). This calculation is typically performed using a least squares method after subtracting the Compton continuum underlying the peak.

GAUSSIAN PULSE SHAPE
A pulse shape resembling a statistical bell-curve, with little or no distortion.

GEOMETRY
The detector to sample distance, the sizes and shapes of the detector, the sample, and any shielding, all of which affect the radiationseen by the detector. The geometry helps define the efficiency of the detector.

GIS
A geographic information system (GIS), also known as a geographical information system, is an information system for capturing, storing, analyzing, managing and presenting data which are spatially referenced.

GRAY [Symbol: Gy]
The SI unit of absorbed dose, defined as one joule per kilogram of absorbing medium.

GROUND STATE
The state of a nucleus, atom or molecule at its lowest energy level.

H

HALF-LIFE [Symbol: Tl/2]
The time in which one half of the atoms of a particular radioactive substance decay to another nuclear form. Half-lives vary from millionths of a second to billions of years.

HISTOGRAM
A representation of data by vertical bars, the heights of which indicate the frequency of energy or time events.

I

INELASTIC SCATTERING
See scattering.

ION
An atom or molecule that has become electrically charged by having lost or gained one or more electrons. Examples of an ion are an alpha particle, which is a helium atom minus its two electrons, and a proton, which is a hydrogen atom minus its single electron.

INDEX
An MCA function that jumps the cursor from one region of interest to another.

INPUT/OUTPUT
The process of loading data into or copying data from an MCA or computer using a peripheral device, such as a computer, a floppy disk, or a printer.

IN SITU COUNTING
Measurement and analysis of radioactivity performed at the sample's location.

INTEGRAL
The total sum of counts in the region of interest.

INTENSIFY
To change the contrast of a displayed region of interest to set it off from data regions of lesser importance.

INTERACTIVE PEAK FIT
The process of refining and verifying the quality of a peak fit. The fitting parameters, such as the centroid location and the way the continuum is defined, can be changed. The change in the quality of the fit is displayed.

INTERFERING PEAK
A peak due to background radiation which is produced at the location of a peak in the sample spectrum or due to a peak produced by a radionuclide in the sample at the location of another radionuclide's peak.

IN VIVO COUNTING
In vivo counting refers to directly measuring and analyzing radionuclide activity levels in a living body.

IN VITRO COUNTING
In vitro counting refers to samples, such as tissue or blood, being analyzed for radionuclide activity levels in an artificial environment (outside of a living body).

I/O
See input/output.

IONIZATION
The process by which an electrically neutral atom acquires a charge (either positive or negative).

IONIZING EVENT
Any process whereby an ion or group of ions is produced. As applied to nuclear spectroscopy, this refers to the passing of radiationthrough a gas, a crystal, or a semiconductor.

ISOMERIC TRANSITION
The de-excitation of an elevated energy level of a nucleus to the ground state of the same nucleus by the emission of a gamma ray or a conversion electron.

ISOTOPE
One of two or more atoms with the same atomic number (the same chemical element) but with different atomic weights. An equivalent statement is that the nuclei of isotopes have the same number of protons (thus the same chemical element) but different numbers of neutrons (thus the different atomic weight). Isotopes usually have very nearly the same chemical properties, but somewhat different physical properties. See also nuclide and stable isotope.

K

keV (kiloelectron volt)
One thousand electron volts.

KEY LINE
Designated in nuclide libraries for reporting purposes only. It is intended to indicate the highest abundance photopeak energy for nuclides with multiple energy lines, or the line that is the least likely to have interferences.

L

LAN
Local area network: a network of two or more computers connected together.

Lc
See critical level.

LIBRARY DIRECTED PEAK SEARCH
Method of designating the location of peaks using all of the lines from the specified nuclide library. All of the nuclide library energies are assumed to have photopeak present and the peak analysis is typically required to verify or reject each peak. This limits the peak search to the nuclides in the library but allows for greater sensitivity than with typical unknown peak searches. See also second difference peak search.

LIMIT OF DETECTION
The minimum amount of the characteristic property being measured that can be detected with reasonable certainty by the analytical procedure being used under specific measuring conditions. If the conditions change, the limit of detection will also change, even if the analytical procedure remains the same. See also lower limit of detection.

LIVE TIME
The time that the ADC is not busy processing a signal. See also dead time and real time.

LIVE TIME CORRECTION
In an MCA, the process of stopping the live time clock whenever the processing circuits are busy and cannot accept further information. Commonly used to extend the collection time by accounting for the dead time.

LOWER LIMIT OF DETECTION (LLD)
The smallest net signal that can reliably be quantified. LLD is a measure of the performance of a system in terms of activity.

LOWER LEVEL DISCRIMINATOR (LLD)
An SCA's minimum acceptable energy level. Incoming pulse amplitudes below this limit will not be passed. See also upper level discriminator.

M

MARINELLI BEAKER
A standard sample container that fits securely over a detector cryostat's endcap and is used when calibrating voluminous samples (usually soil or water solutions).

MASS NUMBER
The sum of the neutrons and protons in a nucleus. It is the nearest whole number to an atom's atomic weight. For instance, the mass number of 235U is 235.

MAXIMUM PERMISSIBLE CONCENTRATION (MPC)
The concentration limit for a given radionuclide in air or water in determining possible inhalation, ingestion or absorption for health physics controls.

MCA
See multichannel analyzer.

MCS
See multichannel scaling.

MDA
Minimum detectable activity. See lower limit of detection.

MEAN
The average of a group of numbers.

METASTABLE ISOTOPE
A long-lived energy state of a particular nuclide that is not its ground state. Some nuclides have more than one isomeric state. An isomeric state has the same mass number and atomic number as the ground state, but possesses different radioactive properties.

MeV (megaelectron volt)
One million electron volts.

MIXER/ROUTER
See analog multiplexer.

MONITORING, PERSONNEL
Periodic or continuous observation of the amount of radiationor radioactive contamination present in or on an individual.

MULTICHANNEL ANALYZER (MCA)
An instrument which collects, stores and analyzes time-correlated or energy-correlated events. See also multichannel scaling and pulse height analysis.

MULTICHANNEL SCALING (MCS)
The acquisition of time-correlated data in an MCA. Each channel is sequentially allocated a dwell time (a specified time period) for accumulating counts until all the memory has been addressed. MCS is useful for studying rapidly decaying radioactive sources.

MULTISPECTRAL SCALING
Multispectral scaling acquisition mode, also called ping-pong mode, alternately collects data in two separate memory regions, quickly collecting many spectra with extremely low latency between acquisitions.

MULTIPLET
Peaks in a spectrum which overlap each other. Compare singlet.

N

NATURALLY OCCURRING RADIOACTIVE MATERIAL (NORM)
Radioactivity that is naturally present in the earth.

NEUTRON [Symbol: n]
An uncharged elementary particle with mass slightly greater than that of the proton, and found in the nucleus of every atom heavier than hydrogen.

NEUTRON ACTIVATION ANALYSIS (NAA)
The process of activating materials by neutron absorption then measuring the emission of characteristic photons on decay to determine the relative abundance of elements in an object.

NID
Nuclide Identification, the process of identifying radionuclides by comparing peak energies detected with entries in a nuclide library.

NIM
Nuclear Instrumentation Module. A nuclear instrument conforming to the DOE/ER-00457T standard.

NOISE
Unwanted signals on or with a useful signal which can distort its information content.

NON-DESTRUCTIVE ASSAY
An analysis method that does not destroy the sample. For example: gamma spectroscopy, X-ray fluorescence and neutron activation.

NUCLEAR SAFEGUARDS
The general topic of maintaining control and accountability of special nuclear materials.

NUCLEUS
The positively charged core of an atom, which contains nearly all of the atom's mass. All nuclei contain both protons and neutrons, except the nucleus of ordinary hydrogen, which consists of a single proton.

NUCLIDE
A general term applicable to the isotopes of all elements, including both stable and radioactive forms (radionuclides).

NUCLIDE LIBRARY
A file listing nuclides, their names, half-lives, types, energies/lines, and line abundances. These files are used with library directed peak searches, nuclide identification (NID) and as aids in performing calibrations.

O

OFFSET, ADC
A digitally performed shift in the ADC's channel zero. Shifts the entire spectrum by the selected amount.

OVERLAP
An MCA function allowing one section of memory to be displayed over another.

P

PAIR PRODUCTION
Creation of an electron- positron pair by gamma ray interaction in the field of a nucleus. For this process to be possible, the gamma ray's energy must exceed 1.022 MeV, twice the rest mass of an electron.

PARAMETER
A variable that is given a constant value for a specific application.

PARENT NUCLIDE
A radionuclide that produces a daughter nuclide during decay.

PASSIVE NON-DESTRUCTIVE ASSAY
A method that uses radiation emitted by the sample itself, without increasing the emission by bombarding the sample with something, such as neutrons. The sample itself is not changed in any way in the course of passive assay.

PEAK
A statistical distribution of digitized energy data for a single energy.

PEAK CHANNEL
The channel number closest to the centroid of a peak.

PEAK FIT
The optimization of parameters to match an expected model shape to empirical data (see also gaussian fit). This optimization is typically performed using a least squares method.

PEAK-TO-TOTAL RATIO
The ratio of the observed counts in a full energy peak to the counts in the entire spectrum, caused by the interaction of radiationwith the detector at that emission energy only.

PERCENT SIGMA [Symbol: s]
An expression of the standard deviation as a percentage. It is numerically equal to 100 times the standard deviation divided by the mean.

PERSONAL AREA NETWORK
A personal area network (PAN) is a computer network used for communication among computer devices (including telephones and personal digital assistants) close to one person. The devices may or may not belong to the person in question. The reach of a PAN is typically a few meters. PANs can be used for communication among the personal devices themselves (intrapersonal communication), or for connecting to a higher level network and the Internet.

PHA
See pulse height analysis.

PHOTOELECTRIC ABSORPTION
The process in which a photon interacts with an absorber atom, the photon disappears completely, and the atom ejects a photoelectron (from one of its bound shells) in place of the photon.

PHOTOELECTRON
An electron released from an atom or molecule by means of energy supplied by radiation, especially light.

PHOTOMULTIPLIER TUBE (PMT)
A device for amplifying the flashes of light produced by a scintillator.

PHOTON
In quantum theory, light is propagated in discrete packets of energy called photons. The quantity of energy in each packet is called a quantum.

PHOTOPEAK
See Peak.

PHYSICAL HALF-LIFE
See half-life.

POLE/ZERO
A method of compensating the preamplifier's output signal fall-time and the amplifier's shaping time constant. Its use improves the amplifier's high count rate resolution and overload recovery.

PMT
See photomultiplier tube.

POSITRON [Symbol: +]
An elementary particle, an "anti-electron" with the mass of an electron but having a positive charge. It is emitted by some radionuclides and is also created in pair production by the interaction of high-energy gamma rays with matter.

POSITRON ANNIHILATION
A process where a positron combines with an electron, producing two annihilation photons of 511 keV each.

PRECISION
The degree of agreement between several measurements of the same quantity under specific conditions. See also accuracy.

PRIMORDIAL NUCLIDE
A nuclide as it exists in its original state.

PROGENY
See daughter nuclide.

PROMPT GAMMA ANALYSIS
A form of neutron activation analysis where gammas, emitted during capture of neutrons, are used for analysis instead of gammas of subsequent beta decay.

PROTON
An elementary particle with a single positive electrical charge and a mass approximately 1837 times that of the electron. The atomic number (Z) of an atom is equal to the number of protons in its nucleus.

PROTON INDUCED X-RAY EMISSION (PIXE)
The emission of X rays when a sample is bombarded by protons. The X rays emitted are characteristic of the elements present in the sample. Used for trace analysis.

PULSE HEIGHT ANALYSIS (PHA)
The acquisition of energy-correlated data in the MCA. Each channel, defined as an energy window, is incremented by one count for each event that falls within the window, producing a spectrum which correlates the number of energy events as a function of their amplitude.

PULSE PAIR RESOLUTION
The ability to discriminate between two pulses close together in time.

PULSE PILEUP
A condition, where two energy pulses arrive at nearly the same time, which could produce false data in the spectrum.

PULSE PILEUP REJECTOR (PUR)
An electronic circuit for sensing the pulse pileup condition and rejecting these pulses so that only single pulses are counted.

Q

QUANTUM
The unit quantity of energy according to quantum theory. It is equal to the product of the frequency of the electromagnetic radiation and Planck's constant (6.626 x 10-34 J/s).

R

RAD
A special unit of absorbed dose. Equal to 0.01 gray.

RADIATION
The emission or propagation of energy through matter or space by electromagnetic disturbances which display both wave-like and particle-like behavior. Though in this context the "particles" are known as photons, the term radiation has been extended to include streams of fast-moving particles. Nuclear radiation includes alpha particles, beta particles, gamma rays and free neutrons emitted from an atomic nucleus during decay.

RADIOACTIVITY
The emission of radiationfrom the spontaneous disintegration (decay) of an unstable nuclide.

RADIONUCLIDE
A radioactive isotope. See also nuclide.

RANDOM SUMMING
A process where the signal from two or more separate decays of the same radionuclide or different radionuclides that occur within the resolving time of the detector end up being recorded together as a single event so that the recorded event is not representative of the original decays. Typically causes counts to be lost from the full energy peaks. Random summing is a function of the overall count rate, or the activity of the sample being measured.

RANDOM SUMMING LOSS
The loss of counts from the full energy peaks due to random summing.

RANGE, ADC
The full-scale address (number of channels) of the ADC's assigned memory segment.

REAL TIME
Elapsed clock time; also called true time. Compare live time.

RECOILING NUCLEUS
A nucleus that gains significant kinetic energy from its decay.

REGION OF INTEREST (ROI)
A user-defined area of the spectrum which contains data of particular interest, such as a peak.

REM (Roentgen Equivalent Man)
A unit of dose equivalency; equal to 0.01 sievert. See also Roentgen.

RESOLUTION
The ability of a spectroscopy system to differentiate between two peaks that are close together in energy. Thus, the narrower the peak, the better the resolution capability. Measured as FWHM.

ROENTGEN
The Roentgen, the international unit of X radiation or gamma radiation, is the amount of radiation producing, under ideal conditions in one cc ionization of either sign equal to one electrostatic unit of charge.

ROI
See region of interest.

S

SCA
Single Channel Analyzer. A device which recognizes events (pulses) occurring between the settings of the lower level discriminator and the upper level discriminator. In an MCA, each event within these limits is counted; events outside of these limits are discarded.

SCATTERING
A process that changes a particle's trajectory. Scattering is caused by particle collisions with atoms, nuclei and other particles or by interactions with electric or magnetic fields. If there is no change in the total kinetic energy of the system, the process is called elastic scattering. If the total kinetic energy changes due to a change in internal energy, the process is called inelastic scattering. See also backscattering.

SCINTILLATOR
A type of detector which produces a flash of light as the result of an ionizing event. See also photomultiplier tube.

SECOND DIFFERENCE PEAK SEARCH
A technique for locating photopeaks by calculating the second difference for each channel in a spectrum, then locating areas of negative concavity. See also library directed peak search.

SEGMENTED GAMMA SCANNER
A gamma spectroscopy system that analyzes a sample by counting it in discrete segments.

SELF ABSORPTION
Absorption of the photons emitted by the radioactive nuclides in the sample by the sample material itself.

SHADOW SHIELD
An attenuating enclosure that shields the detector from direct background radiationwithout being a 4p shield. Typically used in whole body counting.

SHAPE CALIBRATION
The process of establishing a relationship between the expected peak shape and energy. A shape calibration can be established by using two or more peak FWHM/energy (or FWHM/channel) pairs or by using a least squares fit algorithm.

SIEVERT [Symbol: Sv]
The SI unit of dose equivalency (a quantity used in radiation protection). The sievert is the dose equivalent when the absorbed dose of ionizing radiationmultiplied by the dimensionless factor Q (quality factor) and N (product of any other multiplying factors) stipulated by the International Commission on Radiological Protection is one joule per kilogram.

SINGLE CHANNEL ANALYZER
See SCA.

SINGLE ESCAPE PEAK
See escape peak.

SINGLET
A single peak in a spectrum, well separated from other peaks. Compare multiplet.

SMOOTHING
To decrease the effects of statistical uncertainties in computerized spectrum analysis, the content of each channel is replaced by a weighted average over a number of adjacent channels.

SPECIFIC ACTIVITY
The quantity of radioactivity per unit mass; for example, dpm/g or Bq/g.

SPECIAL NUCLEAR MATERIAL (SNM)
Material containing fissionable isotopes suitable for nuclear weapons.

SPECTRUM
A distribution of radiationintensity as a function of energy or time.

SPECTROMETER
A device used to count an emission of radiationof a specific energy or range of energies to the exclusion of all other energies. See also multichannel analyzer.

STABLE ISOTOPE
An isotope that does not undergo radioactive decay.

STANDARD DEVIATION [Symbol: s]
A measure of the dispersion about the mean value of a series of observations expressed in the same units as the mean value.

STRIPPING
Subtracting a specified fractional part of the data in one section of memory from the data in another section of memory.

SYSTEM BUSY TIME
The dead time of an entire spectroscopy system.

T

TOTAL DETECTOR EFFICIENCY
All pulses from the detector are accepted,

TOTAL EFFICIENCY
The ratio of all pulses recorded in the MCA's memory (in all channels) to the gamma quanta emitted by the sample. Compare efficiency.

TRANSURANIC (TRU)
Possessing an atomic number higher than that of uranium (92).

TRUE COINCIDENCE SUM PEAK
A spectral peak, the energy of which equals the sum of the energies of two or more gamma rays or X rays from a single nuclear event.

TRUE TIME
See real time.

U

UNCERTAINTY
In a nuclear decay measurement, uncertainty refers to the lack of complete knowledge of a sample's decay rate due to the random nature of the decay process and the finite length of time used to count the sample.

UPPER LEVEL DISCRIMINATOR (ULD)
An SCA's maximum acceptable energy level. Incoming pulse amplitudes above this limit will not be passed. See also lower level discriminator.

W

WHOLE BODY COUNTING (WBC)
In vivo determination of radionuclide activity levels in the human body. Used to determine compliance with the regulations of various governmental bodies regarding radiationexposure.

Wi-Fi
A term developed by the Wi-Fi Alliance to describe WLAN products that are based on the IEEE 802.11 standards. (See also: Wi-Fi CERTIFIED) .

Wi-Fi CERTIFIED
The certification standard designating IEEE 802.11-based WLAN products that have passed interoperability testing requirements developed and governed by the Wi-Fi Alliance. (See also: Wi-Fi)

Wi-Fi Alliance
A non-profit organization that certifies the interoperability of 802.11 wireless LAN products. Products bearing the Wi-Fi CERTIFIED logo have been proven to work with Wi-Fi products from other vendors. The Alliance also makes sure that certain security and performance features are interoperable, to improve the Wi-Fi user experience.

WINDOW
A term describing the upper and lower limits of radiationenergy accepted for counting by a spectrometer.

X

X RAY
A penetrating form of electromagnetic radiation emitted during electron transitions in an atom to a lower energy state; usually when outer orbital electrons give up some energy to replace missing inner orbital electrons.

Z

ZERO, ADC
An ADC control which aligns its zero energy output with a specific channel in the MCA's memory (usually channel zero).